Port 3443: The 443 Echo — Unassigned but Occupied

What This Port Is

Port 3443 is unassigned. IANA maintains no official service entry for it. No RFC defines a protocol for it. No standards body allocated it to anything.

And yet, it keeps showing up.

The Range It Belongs To

Port 3443 falls in the registered port range (1024–49151). These are ports that applications and vendors can formally register with IANA for a specific purpose. But registration is voluntary, and thousands of ports in this range have never been claimed.

Unregistered ports in this range aren't forbidden territory — they're just unclaimed land. Applications are free to use them, and they often do.

Why Software Lands Here

Port 3443 has an unofficial gravitational pull: it looks like 443.

Port 443 is HTTPS. It's taken — assigned to the global web, unavailable for an application that needs its own local HTTPS listener. So developers reach for something nearby that carries the same visual meaning. Port 8443 is the most common choice. Port 3443 is another.

The result: several unrelated software products independently landed on 3443 for their HTTPS management interfaces.

Acunetix (web vulnerability scanner) runs its entire web UI on https://localhost:3443 by default.¹ The scanner itself, the dashboard, the API for CI/CD integration — all of it comes through this port.

Avid License Control uses port 3443 as its primary port for license activation communication.² If the port is blocked, it falls back to 443.

BMC Monitoring Studio X runs its web interface on 3443.³

Azure API Management uses 3443 for internal configuration traffic from Azure Resource Manager.⁴

None of these products coordinated. They all just needed HTTPS on a non-standard port, and 3443 felt like 443 enough to be the answer.

How to Check What's Using It

If port 3443 shows up on your system, you can find what's listening:

macOS / Linux:

sudo lsof -i :3443

Windows:

netstat -ano | findstr :3443

Then cross-reference the process ID with Task Manager or ps aux to identify the application.

Why Unassigned Ports Matter

The port number system works because most applications respect the assignments. When something is on port 443, you know it's HTTPS. When something is on port 22, you know it's SSH.

Unassigned ports introduce ambiguity. If multiple applications independently claim the same unregistered port, they'll conflict on any machine where both are installed. Port 3443 is lucky — its current occupants (a vulnerability scanner, a license server, a monitoring tool) rarely coexist on the same host.

But it's also a reminder that the port registry isn't a lock — it's a convention. And conventions only work when people follow them.